For example, standard broadcast FM has a peak deviation of 75 kHz above and below the carrier. With stereo FM, the highest modulating frequency (which combines L+R and L-R) is 53 kHz. So most of the energy of standard stereo FM falls in an approximate bandwidth of 2(75+53) = 256 kHz. (Geographically close FM broadcast transmitters are almost always assigned nominal center frequencies at least 500 kHz apart).

Any frequency modulated signal will have an infinite number of sidebands and hence an infinite bandwidth but in practice all significant sideband energy (98% or more) is concentrated within the bandwidth defined by Carson's rule. It is a useful approximation, but setting the arbitrary definition of occupied bandwidth at 98% of the power still means that the power outside the band is only about = 17 dB less than the carrier inside, therefore Carson's Rule is of little use in spectrum planning.